The invention relates to methods of use of gel particles such as beads and spheres.
Gel microcapsules, e.g., of alginate, that contain a relatively small number of living cells have been used to transplant donor cells into host animals in both allografts, i.e., same-species transplants, and xenografts, i.e., different-species transplants. The microcapsules are used primarily in an attempt to immunoisolate the donor cells from the host's immune system. In the case of alginate microcapsules, they include an inner gel core and an outer semipermeable membrane or other coating with a controlled porosity to prevent components of the host's immune system from entering and destroying the cells within the microcapsule cores.
Several methods for microencapsulating cells, e.g., pancreatic islet cells, in alginate gels have been investigated. These include the alginate-polylysine technique described in Lim et al., U.S. Pat. No. 4,391,909 and Soon-Shiong et al., Transplantation, 54:769-774 (1992), the alginate-chitosan system described in Rha et al., U.S. Pat. No. 4,744,933, and the polyacrylate encapsulation method described in Sefton, U.S. Pat. No. 4,353,888. Each of these methods results in alginate gel microcapsules with an outer coating that is distinct from the inner core.
The alginate-polylysine technique, involves extruding a mixture of cells and sodium alginate into a CaCl.sub.2 solution using a droplet generation device to form temporary gelled droplets. These droplets are then coated with positively charged polylysine to form a semipermeable outer membrane or coating around the gelled droplets. Tests have shown that these microcapsules are unstable and produce an inflammatory and fibrotic response when implanted into the peritoneal cavity of animals. However, the addition of a third outer alginate layer over the polylysine membrane has improved the biocompatibility of the microcapsules, resulting in an increase in the duration of islet allograft function in diabetic rodents to more than a year, as described in O'Shea et al., Biochem. Biophys. Acta, 804:133-136 (1984).
Although the alginate-polylysine microcapsules have been shown to prolong the survival of cells in allografts and xenografts, these microcapsules have typically required adjunctive treatment with immunosuppressive agents such as cyclosporin ("CsA"). However, when used in therapeutic, i.e., immunosuppressant, dosages, these agents cause a host of serious side effects including infection, cancer, and renal toxicity. Thus, the use of immunosuppressive agents in therapeutic dosages is undesirable.
Nevertheless, immunosuppressive agents are still used. For example, Soon-Shiong et al., Transplantation, 54:769-774 (1992) and Soon-Shiong et al., P.N.A.S., USA, 90:5843-5847 (1993), describe the use of alginate-polylysine-alginate microcapsules for allografts of canine islets into diabetic dogs, both with continuous or temporary, e.g., 30 day, immunosuppression with CsA. Both sets of dogs remained independent of insulin for an average of over 100 days.
In another report, Soon-Shiong et al., First Int'l Cong. Xenotrans., p. 22 (Minneapolis, MN 1991), describes the prolongation of discordant islet xenograft function in streptozotocin-induced diabetic rats by alginate-polylysine microencapsulation. Microencapsulated canine and human islets were implanted intraperitoneally in the rats and compared to nonencapsulated islet implants. Low dose CsA therapy was instituted in both groups for the duration of the study. Euglycemia was maintained for 43 to 123 days for canine islets, and 42 to 136 days for human islets. In contrast, nonencapsulated islets achieved euglycemia for less than 2 days.
However, there are a few reports of uses of microcapsules without immunosuppression. For example, Weber et al., Transplantation, 49:396-404 (1990), describes a discordant, e.g., from unrelated species, xenograft in which alginate-polylysine microcapsules containing canine islets functioned for an average of only 11.5.about.3 days in diabetic NOD mice. However, immunosuppressive treatment with anti-CD4 monoclonal antibody allowed the cells in some of the recipient mice to remain functional for an average of 83 days.
In addition, Iwata et al., Diabetes, 38 (Supp. 1):224-25 (1988), describes the use of pancreatic islet cells encapsulated in agarose gel microspheres in concordant xenografts, i.e., transplants from different, but closely related species, e.g., rodent-to-rodent transplants, such as hamster cells into mice. No immunosuppressive agent was used in this study, and the two mice remained normoglycemic for 29 and 53 days, respectively.
In a second similar concordant xenograft study, Iwata et al., Transplantation Proc., 24:952 (1992), the immunosuppressive effect of the drug 15-deoxyspergualin on host mice was compared with control mice that received no immunosuppression. Iwata et al. concluded that the agarose microspheres without immunosuppression could not effectively protect the concordant xenografts from rejection, because blood glucose levels indicated that only 2 of 8 xenografts survived over 100 days. However, blood glucose levels indicated that 3 of 5 xenografts survived over 100 days in mice receiving the immunosuppressive drug for 120 days (2.5 mg/kg/day) or 40 days (5.0 mg/kg/day).
In another study, Iwata et al., Transplantation proc., 24:934 (1992), used mouse islet allografts in agarose microspheres to achieve normoglycemia in diabetic mice without immunosuppression. Blood glucose levels indicated that the majority of these allografts survived over 100 days.